394 FOSSIL TURTLES OF NORTH AMERICA. 



Cope regarded these turtles as belonging to Stylemys nebrascensis, the common species of 

 the White River beds of South Dakota. A study of these shells and a careful comparison of 

 them with the South Dakota form has convinced the writer that they are specifically different 

 and, moreover, belong to two distinct species, one of which is the present, the other S. fa fax. 



The only injury that the type specimen suffered during fossilization is a slight lateral 

 compression and a moderate thrusting of the plastron upward toward the carapace. The total 

 length of the carapace (plate 64, fig. i; text-fig. 500) in a straight line is 415 mm.; the width 

 of the shell is 215 mm.; the present height is 170 mm. The original width may have been as 

 much as 300 mm.; the height as much as 1 80 mm. These estimates would make the width of 

 the shell about 72 per cent, of the length. The carapace is high and convex both longitudinally 

 and transversely. Over the bridges the sides were perpendicular or nearly so. There was 

 little or no flare to the anterior and posterior peripherals. In outline, both the front and 

 hinder ends are broadly rounded. Where the sulci crost the free border the latter is mucronated. 

 The nuchal bone is 65 mm. wide along the free border, posteriorly expanding to 95 mm. 

 The first neural is elongated and oval. The second is octagonal; the third is nearly square; 

 the others, hexagonal and mostly with the shorter sides in front. The anterior pygal is bifur- 

 cated. The one behind it is four-sided, its hinder border fitting in a notch in the pygal. The 

 latter bone is somewhat incurved, and is 51 mm. wide and 50 mm. long on the midline. 



The costal plates are alternately wide and narrow, having 

 nearly as high a degree of differentiation as those of the genus 

 TestuJo. The accompanying table presents the widths of the 



Costal. Upper end. 



30 

 48 

 35 

 38 

 3 



Lower end. 



68 



10 



70 



22 



68 

 3 



upper and the lower ends. 



The first and second peripherals have a width of 60 mm. 

 along the free border; their extent backward from this border 

 is 57 mm. The eighth is 70 mm. high and 47 mm. wide. All 

 the free peripherals, as well as the nuchal and the pygal, come 

 down to an acute free edge. An obscure carina crosses the 



bridge peripherals from the free border of the anterior to the free border of the posterior 

 peripheral. 



The nuchal scute is 27 mm. long and 16 mm. wide. The first vertebral is 126 mm. wide 

 in front. The second and third are about 83 mm. wide; the fourth, 72 mm.; the fifth, 1 10 mm. 

 wide posteriorly. On the anterior peripherals the sulci between the marginal scutes and the 

 costals fall considerably below the sutures between the peripheral and costal bones. On the 

 sides and posteriorly the sulci are little below the sutures; on the posterior suprapygal, above 

 the suture. 



The plastron (plate 64, fig. 2; text-fig. 501) has a total length of 360 mm. Its general 

 form is as in 5. nebrascensis. The anterior lobe has a length of 120 mm. and a width of 166 

 mm. at the base. It did not project beyond the front of the carapace. The front of the lip 

 falls within the general curve of the lobe. The lower surface of the lip is flat, while the upper 

 surface curves down to meet it. In S. nebrascensis the upper and the lower surfaces are about 

 equally convex. The entoplastron has the form that it has in S. nebrascensis. The bridge 

 has a width of 150 mm. 



The posterior lobe is 105 mm. long and 180 mm. wide at the base. The notch in the 

 posterior border is somewhat larger than is usual in S. nebrascensis. As to the thickness of the 

 bone, the sloping lateral face behind the inguinal notch, the free border more posteriorly, and 

 the form and proportions of the various scutes, the lobe presents nothing to distinguish it 

 especially from the White River species. 



Another specimen belonging to the Cope collection, No. 1359, presents some differences 

 from the shell just described. The length is 255 mm., the width, 177 mm. The front border 

 is slightly concave in outline. The neurals are nearly as wide as those of the larger specimen 

 just described. The first suprapygal is pentagonal, not bifurcated. The second is 23 mm. 

 high and 56 mm. wide, and appears to include within itself the limbs of the usually bifurcate 

 first suprapygal. There is a rather sharp carina along the sides above the bridge. The 

 anterior vertebral scute is hardly as wide as are the second and the third; while the fifth is but 

 little wider than those just mentioned. 



